All Releases and Versions of SBML Level 2
First, an explanation is in order. The term Releases was introduced in SBML Level 2 Version 3; the Release approach is used to cope with minor editorial changes to specification documents. Prior to that, in Version 2, the same concept existed under the name Revision, but only one revision of Level 2 Version 2 was ever produced. In SBML Level 2 Version 1, the Release/Revision concept was not used at all in SBML specifications.
To make matters simpler, this page lists all previously issued specifications of SBML Level 2, regardless of whether they were Releases of Version 4, or past Versions altogether.
Developers and modelers are strongly encouraged to support the latest Version in any new software development and modeling efforts, as well as to update actively-supported software tools they may be involved in developing or maintaining.
SBML Level 2 Version 4
This is the most recent Release of SBML Level 2.
SBML Level 2 Version 3
SBML Level 2 Version 2
As noted above, SBML Level 2 Version 2 existed in only one Revision.
SBML Level 2 Version 1
As noted above, the use of Releases/Revisions was introduced after Level 2 Version 1 was developed; consequently, there is only one release of Level 2 Version 1.
Note that Version 1 has significant limitations and conceptual gaps. The SBML Editors strongly encourage developers to update existing Version 1-supporting tools to support a later version of SBML Level 2. Similarly, we courage modelers who have models in Version 1 format to update their models to a later Version.